Sensitivity to visible light is a defining parameter of silver halide color photographic materials. For color negative photographic films there continues to be a strong desire to increase this sensitivity. In practice, there are two basic means for improving the response of film to a visible light exposure. On the one hand, the response can be improved by increasing the response of the light-sensitive silver halide emulsion elements used to prepare the film. This may take the form of increasing emulsion grain size, utilizing a more efficient emulsion morphology such as tabular silver halide grains, or improving emulsion sensitization. Increasing emulsion grain size has the drawback that such an increase at a constant amount of coated silver will decrease the number of imaging grains and thus will necessarily result in an undesirable increase in film granularity. Use of an emulsion morphology more efficient at absorbing exposing light such as tabular grains having a high dyed surface area to volume ratio is only beneficial if a sensitization for such grains can be found which will allow the additional absorbed light to be processed by the grain as efficiently as the absorbed light was processed by the emulsion grains being replaced.
A second means of enhancing film sensitivity is to read out more of the information captured by the light sensitive elements already in the film. One method sometimes used to accomplish this is to extend the development time used in processing the film. This method, commonly referred to in the trade as push processing, is, however, not widely employed in high volume commercial processing labs. This is because for maximum throughput, the color processing protocols widely available in the trade such as the KODAK FLEXICOLOR (C-41) process employ a fixed time of development. As a result, commercial color negative films are constructed for optimum performance at the fixed development times employed by the most widely-available commercial processing protocols. Extending the development time for such films usually results not only in increased sensitivity (signal) but also in increased fog density (noise). It would be of great advantage if a means by which the enhanced sensitivity obtained by push processing color negative films could be realized in the widely available commercial color film trade processes such as C-41 and the like at the current fixed development times. It would be of still further advantage if the enhanced sensitivity could be obtained without the increased fog density that usually accompanies this enhanced sensitivity when the development time is extended during push processing.
It is also well known that there is a direct correlation between the sensitivity of color films to visible light and their sensitivity to environmental ionizing radiation. This sensitivity to environmental radiation leads to a decrease in visible light sensitivity and to an increase in minimum (fog) density. A practical means of reducing the negative effects of environmental ionizing radiation on color film sensitivity and fog density is also highly desirable.
Polymers containing sulfonate monomers have been described for controlling viscosity in the various layers in silver halide elements in U.S. Pat. Nos. 5,547,832 and 5,972,591. Polymers containing carboxylic acid monomers have been described as useful for increasing the sensitization width associated with extended time of development in a reversal process for silver halide elements containing monodisperse emulsion in U.S. Pat. No. 7,753,422. Polymers containing sulfonate monomers have also been described Naoi et al. in U.S. Pat. No. 4,710,456 as useful for increasing covering power in black and white photographic films. Naoi does not discuss the use of the polymers in silver halide color photographic materials.
The use of the blue light absorbing dye (Dye-1) as a yellow filter dye in a silver halide color photographic element has been disclosed previously by Shuttleworth et al in U.S. Pat. No. 4,923,788.
There is a continuing need for color silver halide photographic elements having increased sensitivity without a concomitant increase in fog.